The present application is based on Japanese Patent Application No. 2002-121284 filed Apr. 23, 2002, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of detecting an obstacle which interferes with a printing head operable to perform a printing operation on a workpiece such as a work fabric like a T-shirt, and ink-jet printing method and printer wherein the obstacle can be detected.
2. Discussion of Related Art
A silk-screen printer is conventionally used to print a desired image on a work fabric before the printed work fabric is cut and stitched into a desired garment. For instance, the printed fabric is cut and stitched into a T-shirt such that the printed image is located in the front (bosom) or the back of the T-shirt. The printing method using the silk-screen printer is suitable for a relatively large lot production of a relatively small number of kinds of garments in factories, but is not suitable for a relatively small lot production of a relatively large number of kinds of garments which have different unique patterns of printed image desired or selected by the users or consumers.
In view of the above-indicated drawback of the silk-screen printing on work fabrics, various methods of printing desired patterns of image on unprinted garments or cloths have been proposed for producing a relatively wide variety of printed garments in a relatively small lot size. For personal and household printing of unprinted garments, it has been a common practice, for example, to first prepare an intermediate printing medium having an image, and then transfer the image from the medium onto an unprinted garment such that the medium and the unprinted garment are superposed on each other and subjected to a heat and/or pressure for facilitating the transfer of the image from the medium onto the unprinted garment and fixing the image on the garment. The intermediate printing medium is typically a decalcomania paper carrying an image formed by copying or printing with a transferable material, or a special paper carrying an image formed by copying or printing with a transferable toner or ink.
For industrial production of a relatively large number of kinds of printed garments from unprinted garments or cloths in a relatively small lot size, it has been proposed to use a specially designed printer which is connected to a personal computer and operable to print desired patterns of image on unprinted T-shirts or other unprinted garments according to image data stored in a memory of the personal computer. JP-A-5-84887 discloses an example of this type of printer, which has a table provided with an ink jetting device which is fixed on the table and operable to deliver an ink directly on the surface of an unprinted garment held on the table. The ink jetting device includes a printing head which is movable in two mutually perpendicular directions on the unprinted garment, to print the image with the delivered ink.
JP-A-11-227171 discloses an example of a printing device which has an upper belt and a lower belt which cooperate to hold and feed an unprinted garment such as a T-shirt, and a printing head which is movable in a direction perpendicular to the feeding direction of the unprinted garment and operable to deliver an ink on the unprinted garment.
In the printer disclosed in the above-identified publication JP-A-5-84887, the table is provided with a frame arranged to hold the T-shirt or other unprinted garment on the table such that the front and back of the T-shirt, for example, are superposed on each other, that is, two layers of the T-shirt fabric are held in direct contact with each other. In this state, the upper fabric layer (e.g., the front or bosom of the T-shirt) is relatively likely to float away from the lower fabric layer (e.g., the back of the T-shirt) and have some crease. The publication proposes a solution to this problem, namely, proposes to provide a plurality of sensors for detecting distances between the upper surface of the unprinted garment and respective ink heads of the ink jetting device which correspond to respective different colors. The vertical positions of the ink heads are automatically adjusted according to the detected distances, so that the distances of the ink heads to the upper surface of the garment are held constant. However, this arrangement suffers from another problem of increased complexity in the construction and control of the printer.
Where an ink is delivered on the mutually superposed two layers of fabric of the unprinted garment such as the T-shirt, the ink may undesirably permeate through the upper fabric layer into the lower fabric layer, if the fabric has a relatively small thickness or a relatively coarse texture, or if the ink has a relatively low viscosity. The printer using the frame has a further problem that the unprinted garment must be carefully set on the frame such that non-printing portions of the garment such as the sleeves and hem or lower portions are neatly placed on the upper surface of the table, so as to prevent an interference of those non-printing portions with movable components such as the ink heads, that is, so as to prevent the non-printing portions of the garment from being an obstacle to the movable components. The printer in question has another problem due to similar or equal tensioning of the garment held by the frame in all directions irrespective of the direction of weaving of the fabric. Namely, if the fabric of the garment is printed while the fabric held by the frame is elongated in the direction in which the fabric is relatively easily elongated, the image printed on the fabric may deform due to shrinkage of the fabric to the original state after the fabric is removed from the frame.
In the printing device disclosed in the above-identified publication JP-A-11-227171, the ink is delivered onto the garment such as the T-shirt through an opening formed in the upper belt during feeding of the garment while the garment is held in a generally horizontally extending attitude by and between the upper and lower belts, with the upper and lower fabric layers being superposed on each other. Accordingly, like the printer using the frame, the printer using the upper and lower belts may also suffer from undesirable permeation of the ink through the upper fabric layer into the lower fabric layer. Further, this printer tends to be large-sized. In addition, any obstacle which has dropped down through the opening of the upper belt may be present on the garment. This obstacle may disturb the printing operation and deteriorates the quality of an image printed on the garment, and may interfere with any movable components of the printer such as the printing head.
In an ink-jet printer wherein a printing operation is performed on the work fabric set on the upper surface of a planar platen while the platen is moved relative to the printing head in the horizontal plane, local protrusion, floating or creasing of the work fabric may disturb a printing operation performed on the work fabric, deteriorate the quality of an image printed on the work fabric, or interfere with any movable components of the printer such as the printing head, with the local protruding, floating or creasing portion of the fabric being caught between the printing head and the upper surface of the platen. Similar problems may be encountered where any foreign matter or article is left or dropped on the printing surface of the work fabric. The local protruding, floating or creasing portion of the work fabric and the foreign matter are considered to be an obstacle which disturbs the printing operation or interfere with any movable component of the printing head.
It is therefore a principal object of the present invention to provide a method of detecting an obstacle such as a foreign matter existing on a workpiece to be printed by an ink-jet printer, and a local protruding, floating or creasing portion of the workpiece, for preventing the obstacle from disturbing a printing operation performed by the printing head, or from interfering with or damaging any movable components of the printer.
The object indicated above may be achieved according to a first aspect of the present invention, which provides a method of detecting an obstacle that disturbs a printing operation to be performed on a printing surface of a printing portion of a workpiece by a printing head of an ink-jet printer such that the printing head and a planar platen on which the printing portion of the workpiece is set are moved relative to each other between a first position and a second position, with a predetermined spacing maintained between the printing surface of the workpiece and the printing head in a direction perpendicular to the printing surface, the method comprising (a) moving the printing head and the platen relative to each other between the first and second positions; and (b) detecting the obstacle existing on a plane of printing by the printing head, by a sensing device, by scanning the predetermined spacing in a direction intersecting a direction of a relative movement of the printing head and the platen, while the printing head and the platen are moved relative to each other.
In the obstacle detecting method of the present invention described above, the obstacle that disturbs the printing operation performed by the printing head is detected by the sensing device by scanning the spacing between the printing surface of the workpiece and the printing head (in the direction perpendicular to the printing surface) while the printing head and the platen are moved relative to each other. The scanning is effected in a direction intersecting the direction of the relative movement of the printing head and the platen. The present method permits detection of any obstacle which may exists on the plane of printing performed by the printing head. By inhibiting the initiation of the printing operation in the event of detection of any obstacle, the printing head or any other movable component of the printer can be protected against damaging due to an interference with the obstacle. Further, it is possible to prevent deterioration of the quality of an image printed on the workpiece by the printing head.
The sensing device is preferably a light-transmission type sensing device including a light-emitting unit operable to emit a light beam, and a light-receiving unit operable to receive the light beam emitted from the light-emitting unit. However, the sensing device may be a light-reflection type sensing device including a light-emitting unit operable to emit a light beam, and a light-receiving unit operable to receive a portion of the light beam which is reflected by the obstacle.
The light beam emitted from the light-emitting unit of the light-transmission type sensing device may be substantially perpendicular to the direction of the relative movement of the printing head and the platen.
Preferably, the first position is a printing-start position at which the printing operation by the printing head is initiated with initiation of the relative movement of the printing head and the platen, while the second position is a work-setting position at which the workpiece is set on and removed from the platen.
In the arrangement indicated above, the detection of the obstacle by the sensing device is effected during the relative movement of the printing head and the platen between the work-setting position and the printing-start position, so that any obstacle existing in the spacing between the printing surface and the ink delivery surface of the printing head can be detected to prevent damaging the printing head or deterioration of an image printed by the printing head, due to an interference of the obstacle with the printing head.
The sensing device may be arranged to scan the above-indicated spacing to detect the obstacle, while the platen is moved relative to the printing head, from the work-setting position toward the printing-start position, after the workpiece is set on the platen. This arrangement permits detection of any obstacle if existing on the plane of printing, after the workpiece has been set on the platen and before the printing operation is initiated.
For instance, the sensing device is fixedly disposed at a position located between the printing head which is held stationary in the direction of the relative movement of the printing head and the platen, and an end of the platen which is remote from the work-setting position, when the platen is located at the work-setting position. In this instance, the obstacle is detected before the obstacle reaches the printing head, so that the printing head is protected against damaging or functional deterioration due to a collision or interference with the obstacle.
Preferably, the sensing device includes a light-emitting unit operable to emit a light beam, and a light-receiving unit operable to receive the light beam, and the light-emitting and light-receiving units are spaced apart from each other in a lateral direction substantially perpendicular to the direction of movement of the platen relative to the printing head, and are located on opposite, sides of the platen as viewed in the lateral direction when the platen is located in the printing-start position.
The present method may further comprise terminating the relative movement of the printing head and the platen when any obstacle has been detected by the sensing device. Thus, the printing operation is not initiated if any obstacle is detected. It is possible to inform the operator of the ink-jet printer of the existence of the obstacle, or prompt the operator to remove the obstacle from the workpiece or platen or rectify an inadequate setting of the workpiece on the platen.
According to another aspect of this invention, there is provided a method of printing an image on a printing surface of a printing portion of a workpiece by an ink-jet printer including a printing head operable to perform a printing operation on the printing surface, and a platen device which includes a planar platen, the method comprising the steps of:
setting the workpiece such that the printing portion of the workpiece is placed on a surface of the platen;
moving the printing head and the platen device relative to each other between a first position and a second position, with a predetermined spacing maintained between the printing surface of the workpiece and the printing head in a direction perpendicular to the printing surface; and
detecting, by a sensing device, an obstacle which exists on a plane of printing by the printing head and which disturbs the printing operation to be performed on the printing surface by the printing head, such that the obstacle is detected by scanning the predetermined spacing in a direction intersecting a direction of a relative movement of the printing head and the platen device while the printing head and the platen device are moved relative to each other.
According to a further aspect of this invention, there is provided an ink-jet printer including a printing head operable to perform a printing operation on a printing surface of a printing portion of a workpiece, and a platen device including a planar platen on which the printing portion of the workpiece is set, the printing head and the platen device being movable relative to each between a first position and a second position, with a predetermined spacing maintained between the printing surface of the workpiece and the printing head in a direction perpendicular to the printing surface, the ink-jet printer comprising:
a sensing device operable to detect an obstacle which exists on a plane of printing by the printing head and which disturbs the printing operation to be performed on the printing surface by the printing head, the sensing device scanning the predetermined spacing in a direction intersecting a direction of a relative movement of the printing head and the platen device while the printing head and the platen are moved relative to each other.